AWM6100/s door open light comes on shortly after starting

The light comes on about 15-20 secs after starting a wash. If you try the fault diagnosis in the manual, steps 1&2 are ok, press prewash (step 3) and warm fill is ok. The 6100/s doesn't have an easy iron button, so step 4 is not possible. There is water in the drum at this point to the bottom of the window or just above. Press the rinse hold button and it attempts to fill for a second or so and then the door open light illuminates. The drain seems to work ok as this has been repeated a few times and the water has emptied, so it doesn't look as if the pump is faulty and the prewash and main fills are ok. It doesn't do a rinse or spin either as the same indicator comes on.